The science of fear
31 October 2013 Last updated at 07:43 GMT
Halloween has come a long way from the ancient festival of Samhain - from which many of today's traditions are thought to have evolved.
But why do things designed to scare us still hold such enduring appeal?
The BBC's Tim Muffett went to the University of Cambridge to watch the horror film Halloween while his brain was scanned, to see how he reacted - and why.